3. Studies have shown that the time required by workers to complete a certain manual operation follows the normal distribution with mean 26.6 minutes. A group of 35 workers was randomly chosen to receive a special training for 2 weeks. After the training, it was found that their average was 24 minutes with a standard deviation of 3 minutes. Perform a test of hypothesis to determine if the special training lessens the average time for the operation. Use a 5% level of significance